1. Field of the Invention
The present invention relates to a magnetically supported sliding track suited for sliding doors and windows; and, more particularly to a sliding track for a door or window that provides minimal friction for sliding and may be optionally locked by electrical means from any sliding movement.
2. Description of the Prior Art
Many patents address issues related to a magnetically supported sliding window or door. The magnetic supports disclosed in the prior art hang the window or door in a magnetic support and use additional supporting means such as wheels or rods. In such cases, the easy-to-slide door or window is not supported by magnetic repulsion provided at the bottom track of the sliding door or window.
U.S. Pat. No. 4,698,876 to Karita discloses a door apparatus partially supported by a magnetic mechanism. Magnets mounted on the upper surface of the sliding door attract a stationary guide member. Even though the door is supported by four rollers, it is said that the magnetic force is sufficiently strong to limit the loading on the rollers. The sliding door is moved by a moving mechanism. It is the attraction of the magnet to the stationary guide that supports the sliding door weight, not repulsion. There are no magnets at the bottom of the supported sliding door.
U.S. Pat. No. 5,712,516 to Kabout discloses a stator-element for a linear-electrical-drive door provided with a stator-element as such. A stator element of a linear-electric-drive reciprocally slides over a limited length in a straight or curved line of a door, gate or carriage that is provided with a magnet or magetizable counter element. The stator is provided with an elongate holder, a number of rod-like, mutually parallel and adjacent carriers fixed transversely onto the holder. A number of windings each of which is wound around the carrier along a side of the holder and is connected onto a controlled voltage source so that accurate speed control of the body for moving can be obtained. The door is vertically hung by a plurality of magnets attracting a plate that is positioned on the upper portion of the door. The door is moved by an actuator that magnetically moves the sliding door. There are no magnets provided on the bottom of the sliding door that supports its weight.
U.S. Pat. No. 6,289,643 to Bonar discloses a residential motorized sliding door assembly. This motorized sliding door assembly includes a sliding door that slides longitudinally inside an outer support frame assembled in a standard 2×4 stud wall opening in a building. The support frame includes a load-bearing header located horizontally between two vertical posts and opposite a lower threshold. This door is hung vertically on tracks using wheels. A linear motor with coils and a magnet moves the sliding door. The door is not supported by magnetic repulsion. Rather, support for the door is provided by wheels that hang the sliding door from an upper track. No magnets on the bottom of the sliding door support its weight.
Foreign Patent Publication No. DE4016948 to Just et al. discloses a contactless magnetic guidance system for a sliding door. The system exploits mutual repulsion of like poles in radial permanent magnets at the edges of moldings and a guide. The system exploits mutual repulsion of like poles of radial permanent magnets at edges of moldings and a guide. The door is hung from a rod, which is connected to a body that floats inside a tubular passage that has plurality of opposing magnetic poles locating in the bottom portion of the passage, thereby suspending the sliding door and supporting it. The sliding door is displaced by a liner induction motor drive. The sliding door weight is not supported by magnets on the bottom of the sliding door and magnets on a stationary track. Since the magnets support only in the vertical direction, the sliding door is subject to front to back movement, which is not well constrained. Consequently, the body may rub against the tubular passage.
Foreign Patent Publication No. EP897449 to Schuster discloses an electromagnetic drive system for magnetic levitation and carrying systems. A permanent magnet connected to a suspended load is held between two soft electromagnet poles that are energized by a coil. The soft electromagnets are in a state of partial magnetic saturation, which means that the permanent magnet is attracted to both of the soft magnetic poles by magnetic attraction. An equal air gap is said to be maintained on both sides of the permanent magnet by mechanic means. The coils of the electromagnet are energized to change the start of magnetization of the soft magnet pole. The magnet supports the load and is on top, not in the bottom of the suspended load. Magnetic attractive forces support the suspended load; but the load is not supported by magnetic repulsion at the bottom of the load.
Foreign Patent Publication No. JP03244777 to Tsukamoto et al. discloses a magnetic levitation self-running type suspension sliding door. Two electromagnets placed on the upper surface of a sliding door support and drive the sliding door by first monitoring the gap between the electromagnet and the yoke coil directly below it and keeping it the same. The sliding door is uniformly supported thereby. Traveling motion of the door is provided by energizing the yoke coil. Traveling movement requires changes in the magnetic polarity of the yoke coil over which the sliding door rides. These changes sharply reduce the gap between the electromagnet and the yoke coil. No magnets are provided on the bottom of the sliding door, for supporting its weight.
Foreign Patent Application No. JP04007483 to Takahashi et al. discloses an opening and shutting device for magnetic levitation type sliding door. The sliding door is supported on a guide bearing lever, the one end of which rests on a rotatable shaft, while the other end is actuated up or down by magnets, sliding the inclined door one way or other by gravity. The door essentially slides on the guide bearing lever using rollers. No magnetic levitation of the door is indicated since the door hangs from rollers on a guide bearing lever and simply moves back and forth by gravity action as one end of the guide bearing lever is raised up or down by magnetic force. There are no magnets on the bottom of the sliding door supporting the weight of the sliding door.
Foreign Patent Publication No. JP06341267 to Okawa discloses a door opening/closing device. This door is magnetically supported by magnets suspending the door above a track with a gap ‘G’. The magnets are electromagnets supporting the door and disposed in the upper portion of the sliding door. They provide support in the horizontal direction only. It is not clear how the door weight is supported in the vertical direction. The door is moved along the sliding direction by magnetic propulsion. This device can prevent entry of a person through the door. No magnets are operative at the bottom of the door to support the door's weight.
Foreign Patent Publication No. JP08338170 to Kihara discloses a sliding door device. This door has rollers on the top track for sliding of the sliding door. Magnets are placed on either side of the rollers to prevent the sliding door from slipping off of the roller track. The magnets are not disposed on the bottom surface of the sliding door and do not ride on a magnet having the same polarity disposed on a base track on the bottom of the stationary frame.
Foreign Patent Publication No. JP2000179223 to Kotani discloses an installation method for a double sliding door. The bottom portion of the sliding portion has a south magnetic pole while the upper portion of the stationary track has a north magnetic pole. There is thereby created an attractive force, not a repulsive force, which keeps the sliding door within the track. If one of the magnets is an electromagnet, shutting of the electromagnetic current makes it easy to remove the sliding door. This disclosure teaches away from suspending the weight of a door by repulsion between magnets provided at the bottom of the sliding door.
Foreign Patent Publication No. JP2002021427 to Makusamu discloses a sliding door. It appears from the drawing that a magnet provided at the top portion supports the sliding door. Two rollers are provided, presumably supporting the main weight of the sliding door. The magnets are not located on the bottom of the sliding door.
There remains a need in the art for a magnetically supported sliding door or window that is easy to slide back and forth and is immune to dirt accumulation at the sliding tracks provided under the sliding door or window. Moreover, there is a need for securely locking a sliding door or window without having to use latches and locks which are easily defeated by intruders.